This invention relates to diesel engine fuel ignition and more particularly to an injection igniter system which creates a fuel conditioning spark between an injection needle valve and its valve seat upon initial injection of fuel into an engine cylinder to reduce ignition lag.
In a diesel engine, the combustion event is controlled by many factors. Two of these which are fundamental to the process are the compression temperature of the charge and the point at which the fuel is injected. A problem with compression ignition of the fuel in the compressed air charge is that a substantial time lag exists between the initial entry of fuel into the cylinder and the beginning of combustion. This phenomenon, called ignition lag, causes increased levels of NOx to be generated. Also, because of the hammer-like effect caused by the accumulated fuel burning nearly all at once, the engine components must be designed to be more robust than for other engines.
Over the years there have been attempts to reduce the problem of unburned fuel collection prior to compression ignition of the charge. Three of the methods that have been developed are pilot injection, rate shaping and pre-chambers. In pilot injection, a small amount of fuel is first injected into the cylinder prior to the main charge in hope that the pilot charge will start to burn just before the main charge of fuel is injected, thus providing for prompt ignition of the main charge without significant delay. Rate shaping attempts a similar result by initially injecting fuel at a slower rate and increasing the fuel injection rate at a time when the earlier injected fuel has been ignited. In pre-chamber engines, a small amount of fuel is injected into a separate chamber where it is ignited and then causes a jet of burning fuel to be forced into the main combustion chamber to ignite the main charge of fuel. While these methods have their advantages in reducing cylinder pressures and moderating engine structural requirements, they also have disadvantages in control of regulated emissions from the combustion process which make desirable a search for improved ways of accomplishing the reduction of ignition lag in diesel engines.
The present invention proposes to reduce the fuel collection problem in a completely different manner. The essence of the concept is to supply enough energy at the point of initial fuel entry into the cylinder that the fuel is placed in condition for immediate ignition in the compressed air charge of the engine cylinder. There are many ways in which this energy could be supplied including, for example, laser beam, induction, microwave, AC spark, DC spark, radiation, resistance heating, chemical reactions, etc. In the presently preferred embodiment, the selected method is by creating a spark or electrical discharge at the point of initial fuel entry into the cylinder so that the fuel is conditioned by the spark energy to be ready for compression ignition upon entry into the cylinder.
To provide means for spark conditioning of the injected fuel with a minimum of modification of conventional diesel engine components, the present invention provides a diesel igniter injector or igniter fuel nozzle. The igniter nozzle is constructed so that an electrical charge may be imposed between the injection valve seat in the injector nozzle tip and the injection valve which seats upon the valve seat and is opened to allow fuel to be injected. The injection valve and associated moving components, such as a biasing spring, are preferably insulated from the body of the injector or fuel nozzle and are connected electrically with an external source of electrical energy. The electrical system is arranged such that, upon lifting of the injection valve off the valve seat, the electrical charge between the valve and the associated nozzle creates a spark, or electrical discharge arc, between the tip of the injection valve and the valve seat, between which the fuel is passing as it is injected. The electrical discharge across this gap is believed to cause fuel cracking, ionization and heating, all of which condition the fuel such that upon entry into the cylinder it will be ignited quickly with little or no ignition lag. Thus, as additional fuel is injected into the cylinder, it will begin its combustion event, and a rapid rise in cylinder pressure beyond that caused by the rate of fuel injection will be avoided. Also, combustion will be better controlled and reduction in undesirable emissions such as NOx can be expected.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.